Plasma ADA enzyme activity is increased in patients with hypoxia. (A) To develop a technique for measuring ADA activity in plasma, different concentrations of adenosine were added to the plasma and assessed for dCF-inhibited inosine generation. Optimal resolution was found with using 20 μM adenosine (black line indicates plasma alone; gray line, plasma after addition of 20 μM adenosine). (B-C) VEGF and ADA are increased in the plasma of patients with hypoxia. Plasma samples were obtained from 10 pediatric patients with chronic hypoxia (mean oxygen saturation of 82%) undergoing cardiac surgery (bidirectional Glenn procedure) and 10 age- and sex-matched controls (mean oxygen generation of 96%) undergoing noncardiac surgery. Plasma VEGF was measured with standard ELISA technique. ADA activity was measured via HPLC as percent adenosine conversion to inosine. *Significant differences with hypoxia (P < .01). #Differences with dCF treatment (100 nM; P < .001). (B-C) Error bars indicate SD. (D) Correlation of ADA plasma activity with VEGF plasma levels displayed for individual patients (▪, hypoxia) and control patients (•, normoxia). Note the strong correlation between ADA activity and circulating VEGF levels (r2 = .89, P < .01). The diagonal represents the linear regression line.
